the Blanzy collieries. It is a circular saw 5 feet (1.50 m.) in diameter, with 28 removable cutters, all of one shape, upon its circumference. The cutters are arranged in fours, so that four of

them cover the whole width of the holing, which is 3 inches (7.6 cm.) high. Two small compressed air engines, inside the waggon which carries the saw, drive a horizontal pinion, which gears into the spaces between the cutters; in fact, the saw is a cog wheel with a cutter inserted into each tooth. The depth of the holing is 4 feet. The total weight of the machine is 35 cwt. (1800 kil.)

(4) Endless chain with cutters attached.-Baird's machine,* which is used both for coal and ironstone, is of this type. A carriage moving on rails supports two cylinders worked by compressed air, and these set in motion an endless chain with cutters, which revolves round two pulleys, one at each end of a jib or arm. The jib can be made to extend under the seam for a distance varying from 2 feet 9 inches to 5 feet, and the groove which is cut is only 2 inches high.

It is stated that a machine will make an undercut 2 feet 9 inches deep by 100 yards long in 8 or 10 hours.

(5) Wire Saw.-The most novel method of cutting stone is one which has been used at marble quarries in Belgium and el-ewhere, and is called by the inventor the Helicoidal Saw System.

It consists in sawing grooves by an endless cord, composed of three steel wires twisted together, which travels on the rock, and is supplied with sand and water. The sand is drawn along by the spaces between the wires, and will cut even very hard stone. At present only vertical grooves have been cut; the first process consists in sinking two pits for receiving the pulleys which guide the cord in making its cut, and which have to be lowered as the cut is deepened. The pits are bored 2 feet 4 inches (700 mm.) in diameter by cylinders of sheet-iron, with the lower and cutting edge made of sheet steel. The cylinder is made to rotate at the

rate of 100 to 180 revolutions a minute by a vertical axis set in motion by a horizontal pulley at the top, driven by a wire rope, whilst sand and water are fed in to the cutting edge. As the annular groove is cut deeper and deeper, the cylinder is gradually lowered by a little winch and two wire ropes. The cylinders now in use are constructed so as to cut to a depth of 10 feet 9 inches (3.30 m.). When this cut has been made, a core remains, which can easily be broken off at the bottom and lifted out. In the case of marble the core can be utilised and sold as a column. If there is a demand for smaller columns, boring cylinders of less diameter are used, and two or four holes are bored side by side. After the removal of the columns the thin intervening partitions of rock are broken down, and space enough is afforded for the introduction of a pulley and a frame.

Two of these pulley-pits are prepared at the two extremities of the line along which it is desired to make a saw-cut, which may be 50 feet or more in length, if required, and the carriers are then inserted. The carrier, made of channel iron, supports two pulleys, each 2 feet in diameter; one is fixed at the top, whilst the second is so arranged that it can be lowered by a large screw. The cord for sawing in the quarry is about inch (6 mm.) in diameter, made up of three wires of mild steel, twisted together so

as to form a strand. It is driven at the rate of 13 feet (4 m) per minute, and will deepen the cut in marble at the rate of 3 to 4 inches or more per hour. The friction of the spiral wires on the pulleys and rock causes the cord to revolve a little as it is carried forwards, and all parts of it are thus equally worn. When it is so much worn that it no longer presents spiral spaces which will

hold sand, it has to be changed. If it breaks while in use, it can very easily be spliced.

Fig. 217 represents the arrangement adopted at the Traigneaux* Quarry, near Philippeville, Belgium. A B C D E F is the wire cord travelling in the direction shown by the arrows; H and G are the two pits which have been bored to hold the pulley-frames. When the cutting process began, the wire cord would have been running along the line I J; the groove is gradually deepened until at last it reaches the line K L.

When suitable vertical cuts have been made, the block is severed horizontally by means of wedges.

(6) Revolving Bar with Cutters.-Under this head may be classed the Bower, Lechner, and Legg machines, all of which have been designed for holing coal.

Bower's machine consists of a bar 3 feet long, armed with steel teeth, which is made to revolve at the rate of 600 to 800 revolutions a minute by an electric motor. The bar rapidly cuts away a groove as the motor is made to travel along the rails; the groove is 5 inches high in front, and 3 at the back.†

In the Lechner and Legg machines the cutting bar lies parallel to the line of the face, and not at right angles to it, as in Bower's coal-cutter.

V. Machines for Excavating Complete Tunnels -Hitherto machines of this kind have been little used. Three may be mentioned-viz., the Beaumont, Brunton, and Stanley tunnellers.

The Beaumont machine has received a good deal of notice, owing to its having been employed in the Channel Tunnel. It consists of a very heavy horizontal iron shaft, which is made to revolve by compressed air engines. The shaft carries a cross-head armed with teeth, which cut away the whole face by a series of concentric grooves. The chips are made to fall on to an endless chain with buckets, and are thus conveyed to a waggon behind the machine, so that no interruption of the work takes place for loading. The machine travels forward in a cradle which fits the bottom of the circular tunnel, and when the limit of advance is reached, the machine is lifted up by screw-jacks, and the cradle is once more brought under it, so that a new cut can be begun.

Like the Beaumont machine, Brunton's tunneller § excavates a circular drift by chipping away the whole face, but in this case the work is done by steel-cutting discs about 10 to 20 inches in diameter, and from inch to 1 inch thick. As yet it has been little used.

#

Copied from a pamphlet published by the Société anonyme internationale du fil helicoidal. Brussels, 1888.

+ G. B. Walker, “Coal-getting by Machinery,” Proc. Fed. Inst. Min. Eng., vol. i. p. 129.

Eng. Min Jour., vol. xlvi. (June 1888), p. 399. § Jour. Soc. Arts, vol. xxii. (1873-74), P. 404.

Stanley's tunneller (Fig. 218), on the other hand, is a comparatively new machine already doing good work in driving headings in coal. It consists in the main of a strong central shaft, which carries a cross-head with two projecting arms. At the end of each arm are three steel teeth or cutters. The central shaft is made to revolve by a pair of small vertical compressed air-engines, and the teeth cut away an annular groove 3 to 4 inches wide. The chips

FIG. 218.

are brought out by scrapers attached to the arms which carry the teeth. The advance of the cutters is caused by the forward movement of the main central shaft; this is screwed outside, and works in a nut attached to the frame. The rate of advance is therefore determined by the pitch of this screw and the speed with which it is made to turn round.

After boring the annular groove to the depth of a foot or so, large lumps of the central core break off, and the machine is stopped to get them out. Work is then resumed till the arms have penetrated to their full length. The machine is stopped, the remaining part of the core is wedged out and cleared away, and now the frame is run forward and fixed for another cut. The rate of progress when working in coal is about 1 yard per hour, and during a trial of 24 hours the machine cut a tunnel 64 feet 6 inches in length. The diameter of the headings or tunnels is 5 feet. A machine for working in harder rock with a slower cut is being tried.

Stanley has also made a modification of his tunneller in which the whole of the face is cut into little pieces; the chips are carried off by an Archimedean screw and delivered into a waggon at the back.

MODES OF USING HOLES FOR BREAKING GROUND.-After holes have been bored, either by hand or by machinery, a force of some kind has to be applied inside them in order to produce a rending action. The commonest method is to employ an explosive, but the treatment of the subject would not

be complete without a brief mention of some other processes.

Holes may

receive:

1. Wedges.
2. Water.

3. Wooden plugs.

4. Compressed air cartridges.

5. Hydraulic cartridges.

6. Lime cartridges.

7. Explosives.

1. Wedges. When a hole has been bored, a compound wedge can be inserted which can do the work of splitting with far greater ease than a single wedge driven into a mere crack in the rock. The combination of three wedges is known as the plug and feathers, a flat wedge, the plug, being inserted between the feathers, which have the outer face curved. The feathers are placed in the hole and the plug is driven down between them with a hammer or sledge.

Varieties of this simple apparatus, in which the wedge or the feathers are moved by hydraulic pressure or by a screw worked

FIG. 219.

อ

by hand, have been used for getting down coal. Fig. 219 is the Elliott multiple wedge of the Hardy Patent Pick Company.

2. Water. In cold climates the expansion of water in freezing can be utilised for rending rocks in open quarries. A row of holes is bored in the line along which it is wished to split off a block of stone, the holes are filled with water and well stopped with wooden plugs; when the water is converted into ice, the block splits off. 3. Wooden Plugs.-Dry oaken plugs are driven into holes and then watered. The wood expands and causes a fracture.

4. Compressed Air.-Air compressed to about 400 lb. per square inch has been employed experimentally in the place of gunpowder for breaking down coal.

a flat

5. Hydraulic Cartridges.-Levet proposes to use metallic tube placed in a borehole, which is rammed up tightly. The flat metallic cartridge is then connected with an hydraulic press, and as soon as this is worked the cartridge expands, and the coal is broken off.

6. Lime Cartridges. This plan is mentioned with the two last, not because it is employed in mines at the present time, but simply to complete the series of methods of applying a rending force in boreholes.

A small iron pipe is first placed in the borehole, which is 2 inches in diameter, and then a cartridge of compressed lime